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CS5253B-1 Datasheet(PDF) 8 Page - ON Semiconductor |
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CS5253B-1 Datasheet(HTML) 8 Page - ON Semiconductor |
8 / 10 page CS5253B−1 http://onsemi.com 8 VOUT is in regulation. Further increase in the supply voltage brings the pass transistor out of dropout. In this manner, any output voltage less than 13 V may be regulated, provided the VPOWER to VOUT differential is less than 6.0 V. In the case where VCONTROL and VPOWER are shorted, there is no theoretical limit to the regulated voltage as long as the VPOWER to VOUT differential of 6.0 V is not exceeded. There is a possibility of damaging the IC when VPOWER − VOUT is greater than 6.0 V if a short circuit occurs. Short circuit conditions will result in the immediate operation of the pass transistor outside of its safe operating area. Overvoltage stresses will then cause destruction of the pass transistor before overcurrent or thermal shutdown circuitry can become active. Additional circuitry may be required to clamp the VPOWER to VOUT differential to less than 6.0 V if fail safe operation is required. One possible clamp circuit is illustrated in Figure 21; however, the design of clamp circuitry must be done on an application by application basis. Care must be taken to ensure the clamp actually protects the design. Components used in the clamp design must be able to withstand the short circuit condition indefinitely while protecting the IC. Figure 21. This Circuit Is an Example of How the CS5253B−1 Can Be Short−Circuit Protected When Operating With VOUT > 6.0 V VCONTROL VPOWER VSENSE VOUT VADJ External Supply External Supply CS5253B−1 Stability Considerations The output compensation capacitor helps determine three main characteristics of a linear regulator: loop stability, startup delay, and load transient response. Different capacitor types vary widely in tolerance, Equivalent Series Resistance (ESR), Equivalent Series Inductance (ESI), and variation overtemperature. Tantalum and aluminum electrolytic capacitors work best, with electrolytic capacitors being less expensive in general, but varying more in capacitor value and ESR overtemperature. The CS5253B−1 requires an output capacitor to guarantee loop stability. The Stability vs ESR graph in the typical performance section shows the minimum ESR needed to guarantee stability, but under ideal conditions. These include: having VOUT connected to VSENSE directly at the IC pins; the compensation capacitor located right at the pins with a minimum lead length; the adjust feedback resistor divider ground, (bottom of R2 in Figure 20), connected right at the capacitor ground; and with power supply decoupling capacitors located close to the IC pins. The actual performance will vary greatly with board layout for each application. In particular, the use of the remote sensing feature will require a larger capacitor with less ESR. For most applications, a minimum of 33 mF tantalum or 150 mF aluminum electrolytic, with an ESR less than 1.0 W overtemperature, is recommended. Larger capacitors and lower ESR will improve stability. The load transient response, during the time it takes the regulator to respond, is also determined by the output capacitor. For large changes in load current, the ESR of the output capacitor causes an immediate drop in output voltage given by: DV + DI ESR There is then an additional drop in output voltage given by: DV + DI T C where T is the time for the regulation loop to begin to respond. The very fast transient response time of the CS5253B−1 allows the ESR effect to dominate. For microprocessor applications, it is customary to use an output capacitor network consisting of several tantalum and ceramic capacitors in parallel. This reduces the overall ESR and reduces the instantaneous output voltage drop under transient load conditions. The output capacitor network should be as close to the load as possible for the best transient response. Protection Diodes When large external capacitors are used with a linear regulator, it is sometimes necessary to add protection diodes. If the input voltage of the regulator gets shorted, the output capacitor will discharge into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage, and the rate at which VCONTROL drops. In the CS5253B−1 regulator, the discharge path is through a large junction and protection diodes are not usually needed. If the regulator is used with large values of output |
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Similar Description - CS5253B-1 |
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